With So Many Seasonal Floods,

that occur in so many countries, 

I thought this a neat idea, temporary dams, the above picture is not photoshopped, and was taken in Grein, Austria, and it certainly seems to be doing the job of keeping flood waters out,

and this is how it is constructed, for more details have a look here, the dam can be made up to 4.5 meters high! what a neat idea to solve an occasional seasonal problem.